1. Field of the Invention
This invention relates to a magnetic tape wind-up control method for controlling the tension on a magnetic tape when the magnetic tape is fed from a feed reel and wound around a wind-up reel. This invention particularly relates to a magnetic tape wind-up control method wherein the speed at which the feed reel is rotated is controlled, and the tension on the magnetic tape is controlled on the side of the wind-up reel so that the magnetic tape is wound up accurately with little fluctuation in the tension on the magnetic tape. This invention also relates to a tape wind-up control method wherein the speed at which a tape is moved from a feed reel to a wind-up reel is controlled in accordance with a predetermined reference speed pattern.
The present invention further relates to a tape wind-up apparatus for controlling a long tape delivered from a feed reel so that the tape travels at a constant speed, and more particularly to a tape wind-up apparatus for winding up a predetermined length of a long original tape wound about a feed reel on a series of wind-up reels.
2. Description of the Prior Art
When magnetic tapes are fed from feed reels and wound around wind-up reels in accordance with a predetermined speed pattern, the tension on the magnetic tapes which are being wound around the wind-up reels should be controlled in accordance with a predetermined pattern. For this purpose, conventional apparatuses for winding up a magnetic tape are constituted as shown in FIG. 11. With reference to FIG. 11, a magnetic tape 2 fed from a feed reel 1 is threaded over a counting roller 3 and a dancing roller 4, and is wound around a wind-up reel 5. The counting roller 3 is positioned so that it is in contact with the magnetic tape 2, and is rotated as the magnetic tape 2 is moved, thereby allowing the length over which the magnetic tape 2 has been fed, and the feed speed at which the magnetic tape 2 is fed to be detected. The dancing roller 4 is rotatably supported on a dancer arm (not shown) and is urged by an arm spring (not shown) in such a way that it pulls out the magnetic tape 2 which is guided by a pair of guide rollers 6 and 7. The feed reel 1 and the wind-up reel 5 are rotated respectively by a feed motor 8 and a wind-up motor 9.
On the other hand, a reference speed value Vref and a reference tension value Tref are respectively stored in ROM's 10 and 11. A signal which represents the reference speed value Vref is fed into a differential amplifier 14 via a D/A converter 12. A signal which represents the reference tension value Tref is fed into a differential amplifier 15 via a D/A converter 13. Also, a signal representing the feed speed of the magnetic tape 2 which feed speed is detected by the counting roller 3 is fed into the differential amplifier 14, and a signal representing the tension on the magnetic tape 2 which tension is detected from the position of the dancing roller 4 is fed into the differential amplifier 15. The differential amplifier 14 calculates the difference between the reference speed value Vref and the detected feed speed of the magnetic tape 2. The differential amplifier 15 calculates the difference between the reference tension value Tref and the detected tension on the magnetic tape 2. The differences are fed into servo amplifiers 16 and 17 in order to control the speeds at which a feed motor 8 and a wind-up motor 9 are rotated, so that the feed speed and the tension on the magnetic tape 2 become equal to the reference values.
One of such means for controlling the tension on the magnetic tape is disclosed in Japanese Unexamined Patent Publication No. 57(1982)-78664. The disclosed means predicts the length of the magnetic tape which length is required in a vacuum column, and feeds the predicted length of magnetic tape into the column during quick tape movement operations.
However, the conventional magnetic tape wind-up control method has the problems described below. FIGS. 12A through 12E are graphs showing characteristics of a conventional apparatus for winding up a magnetic tape. The speed command voltage V fed to the feed motor 8 changes as shown in FIG. 12A from the point at which the motor begins to rotate to the point at which it stops rotating. At this time, a graph of the current I flowing into the feed motor 8 should appear as shown in FIG. 12B. However, actually, because a braking force which is proportional to the speed of rotation of the motor 8 is applied as shown in FIG. 12C, the graph of the current I flowing into the feed motor 8 actually appears as shown in FIG. 12D. Therefore, as indicated by the solid line in FIG. 12E, the tension on the side of the wind-up reel 5, which is detected from the position of the dancing roller 4, deviates from the reference tension value Tref indicated by the broken line. Specifically, when the voltage fed to the feed motor 8 is increasing in value (the acceleration zone in FIG. 12A), the position of the dancing roller 4 is lower than the reference position, and the dancing roller 4 is gradually moved down. Thereafter, at the end of the acceleration zone, the dancing roller 4 is moved up in such a way that a discontinuity is created in the graph of the tension. In the constant speed zone, the dancing roller 4 is kept at a position slightly lower than the reference position. Thereafter, in the deceleration zone, the dancing roller 4 is gradually moved up to a position higher than the reference position. Accordingly, with the conventional magnetic tape wind-up control method, the tension on the magnetic tape 2 cannot be controlled accurately and made equal to the reference tension value Tref.
The technique disclosed in Japanese Unexamined Patent Publication No. 57(1982)-78664 is designed to control the tension on the magnetic tape with a vacuum column, and is different from the technique of the present invention.